The present invention relates to a method of producing a shadow mask for use in a color cathode ray tube.
In general, a shadow mask for use in a color cathode ray tube has a multiplicity of minute holes arranged regularly. In operation of such a color cathode ray tube, less than one-third (1/3) of the emitted electron beams can pass through these minute holes, while other portions of the electron beams are made to collide with the structural portions of the shadow mask. In consequence, the temperature of the shadow mask is raised with the result that the color purity is degraded due to a thermal distortion of the shadow mask.
Under these circumstances, various studies and proposals have been made in order to suppress any deviation of beams caused by thermal distortion of the shadow mask. For instance, it has been proposed to use, as the material of a shadow mask, an Fe-Ni alloy, which has a small thermal expansion coefficient so as to reduce the thermal distortion of the shadow mask, as shown in Japanese Unexamined Patent Publication No. 59861/1984.
It is true that shadow masks made of conventional Fe-Ni alloys exhibit small amounts of thermal distortion, but are inferior in the mechanical strength. In consequence, the shadow masks made of such materials tend to be deformed in the course of manufacture of the shadow mask or in the subsequent assembly of cathode ray tubes, as well as during handling or transportation, with the result that the color purity is impaired undesirably.
These have been also made various proposals and attempts such as an improvement in the structural design of the shadow mask, construction for mounting the shadow mask on a mask support, and so forth. Unfortunately, all these attempts and proposals are still unsatisfactory and cannot provide any appreciable effect.